Among the apparatuses using a photosensitive sheet, there are known the copying machine of the electrostatic image transfer type, the laser printer, the full color printer, etc. The copying operation of a copying machine of the electrostatic image transfer type, which is widely used in a copying machine, will be described.
A copy paper is fed into the main body of the copying machine from paper feeding cassettes or the like, waits so as to be in synchronization with the photosensitive sheet mounted for example in a belt shape, and is then caught in with and comes in contact with the aforementioned photosensitive sheet that is in a rotating state. The toner image of the sheet is then transferred on to the copy paper, the fixing process of the toner is further performed through heat and other method, and the copy paper is discharged outside the main body of the copying machine thereafter. As to the photoconductor belt that completed the transfer operation on to the copy paper, it goes through the stages of cleaning for removing the remaining toner, static elimination, electrostatic charge, exposure and developing, and transfers the newly formed toner image on to the copy paper thereafter.
However, there also exists an image forming apparatus operating according to a principle different from the reproduction of the electrostatic image transfer type. In this copying machine that is one type of image forming apparatus, a photosensitive sheet 2 stored in a roll shape is sent forward on and an image is formed on a copy paper 25 by pressing the photosensitive sheet 2 and the copy paper 25 together, as illustrated in FIG. 10. Namely, the photosensitive sheet 2 is made of a photosensitive and pressure sensitive material, and a multiplicity of microcapsules having a diameter of about 10 to 20 .mu.m containing leuco ink and light hardenable substance, are coated on a light reflective metallic sheet of aluminum (A1) or other metal. As to the aforementioned copy paper 25, it is coated with a developer that colors in reaction with leuco ink.
A copying machine such as described above, is provided on its top with an original document platen 3 composed of a hard transparent glass. Below the original document platen 3 there is installed a first optical unit 6 capable of moving in the directions A and B, composed of light sources 4 that irradiate light toward an original document placed on the original document platen 3, and a reflection mirror 5 that leads the reflected light from the original document to a reflection mirror 7.
A second optical unit 9 is composed by the above-mentioned reflection mirror 7 and a reflection mirror 8 placed in a diagonal direction opposite to the direction of the reflection mirror 7. Provision is made so that in the second optical unit 9, the aforementioned reflected light is led toward a lens 10. The aforementioned reflected light passes through the lens 10, is reflected thereafter by a reflection mirror 11, and is irradiated on the photosensitive sheet 2 described earlier.
The photosensitive sheet 2 is supported by a feed shaft 13 located inside a cartridge 12 so as to be capable of rotating freely. An edge of the photosensitive sheet 2 passes successively on guide rollers 14 and 15 located inside the cartridge 12, a tractor roller 16, an exposure plate 20, a buffer roller 17 mounted so as to be able to move in the directions C and D, and between pressure rollers 18a and 18b of a pressure development device 18, and is then wound on a winding roller 19 installed inside the cartridge 12.
Moreover a leader sheet is attached to the forefront portion of an edge of the photosensitive sheet 2. When starting to send the photosensitive sheet 2 forward, the photosensitive sheet 2 may be prevented from slipping off from the proper forwarding direction by fitting forwarding holes formed in a line on both sides of the leader sheet, on forwarding pins 16a mounted and protruding on the circumference of the tractor roller 16 mentioned earlier.
The transportation system of the copy paper 25, from the feeding to the discharge, will be described. Sheets of copy paper 25 are piled up in paper feeding cassettes 21, 2 and 23. The top copy paper sheets 25 of the paper feeding cassettes 21, 22 and 23, are fed into the copying machine 1 by feeding rollers 26, 27 and 28 respectively. The copy paper 25 that was fed into the copying machine 1 goes through a paper stop roller 29, that synchronizes the copy paper 25 with the photosensitive sheet 2, passes between the aforementioned pressure rollers 18a and 18b, then reaches a glossing device 30 provided with a heat roller 30a, and after the developer is fixed in the glossing device 30, is discharged on a paper discharge tray 32 by a paper discharge roller 31.
The exposure driving system of the copying machine 1 outlined above, will be described. The buffer roller 17 is moved at a prescribed speed in the direction D, while the pressure development device 18 is kept in a suspension state and the feed shaft 13 is ready to rotate. The prescribed speed at this time, is determined according to the copy magnification and the original document scanning speed, that is the travel speed of the first optical unit 6. In concrete terms, when the copy magnification is set at full size and the original document scanning speed is V.sub.1, the buffer roller 17 is moved in the direction D at a speed 1/2 V.sub.1 so that the transportation speed of the photosensitive sheet 2 on the exposure plate 20 equals V.sub.1.
After the exposure operation described above is completed, the buffer roller 17 stops moving, then the feed shaft is locked so that it does not rotate any more, and the pressure development device 18 starts rotating. Accordingly, the photosensitive sheet 2 whereon a latent image was formed through the aforementioned exposure operation, is conveyed by the pressure development device 18. At this time the buffer roller 17 is pulled by the photosensitive sheet 2 and moves in the direction C. Meanwhile, the copy paper 25 that was sent by the feeding roller 26 and the like during the feeding operation of the copy paper 25, is synchronized with the photosensitive sheet 2 whereon the latent image is formed, at the paper stop roller 29 and is conveyed. The copy paper 25 is then superposed with the photosensitive sheet 2 in the pressure development device 18, and an image is formed on the copy paper 25. In the image forming process, the microcapsules of the photosensitive sheet 2 that did not harden yet and that are distributed in correspondence with the latent image, are broken by the pressure rollers 18a and 18b, the leuco ink that was contained therein flows out to react with the developer on the copy paper 25 to develop colors, thus forming the image.
The copy paper 25 that passed through the image forming process, then proceeds to the glossing device 30. After the image fixing operation is performed in the glossing device 30 by boosting the coloring and making the resin previously coated on the copy paper 25 even, the copy paper 25 then moves on to the discharge process, and is discharged on the paper discharge tray 32 by the paper discharge roller 31.
However, as described earlier, a leader sheet is attached at the forefront portion of an edge of the photosensitive sheet 2, and when starting to send the photosensitive 2 sheet forward, the photosensitive sheet 2 is prevented from slipping off from the proper forwarding direction by fitting successively the forwarding holes formed in a line on both sides of the leader sheet, on the forwarding pins 16a of the tractor roller 16.
Nevertheless, the copying machine presents the disadvantage that fitting the forwarding holes on the above-mentioned forwarding pins 16a is not easy, as the leader sheet is of a firm texture, thus the initial loading operation cannot be performed quickly. Also, the forwarding holes sometimes happen to be fitted in a shifted manner, causing the photosensitive sheet 2 to be sent slantwise, or further, one side of the photosensitive sheet 2 to loosen, or the like.